Physiological measurement systems employed in healthcare often feature visual and audible alarm mechanisms that alert a caregiver when a patient's vital signs are outside of predetermined limits. For example, FIG. 1 illustrates a pulse oximeter, which measures the oxygen saturation level of arterial blood, an indicator of oxygen supply. A typical pulse oximetry system 100 has a sensor 101 that provides a sensor signal 162 to a pulse oximeter (monitor) 102. The sensor 101 has emitters 110 and a detector 120 and is attached to a patient at a selected fleshy tissue site, such as a fingertip. The emitters 110 transmit light having red and IR wavelengths into the tissue site. The detector 120 generates the sensor signal 162 in response to the intensity of the emitter transmitted light after attenuation by pulsatile blood flow within the tissue site A pulse oximetry sensor is described in U.S. Pat. No. 6,088,607 entitled Low Noise Optical Probe, which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.
The monitor 102 has drivers 140, a controller 150 and a front-end 160. The drivers 140 activate the emitters 110 according to the controller 150, and the front-end 160 conditions and digitizes the resulting sensor signal 162. The monitor 102 also has a signal processor 170, a display 180 and an alarm 190. The signal processor 170 inputs the conditioned and digitized sensor signal 164 and calculates oxygen saturation along with pulse rate, as is well-known in the art. The display 180 provides a numerical readout of a patient's oxygen saturation and pulse rate. The alarm 190 provides an audible indication when oxygen saturation or pulse rate are outside of preset limits. A pulse oximetry monitor is described in U.S. Pat. No. 5,482,036 entitled Signal Processing Apparatus and Method, which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.